Top 10 Most Dangerous Drugs

dangerous drugs

Let's take a look on the most dangerous drugs, their drug class, important interactions, contraindications and side-effects. We are also going to point out some of the common pitfalls that you may experience as a doctor or as part of your prescribing safety assessment. You'll feel more confident about these key medications on the wards.


Let's start with Warfarin. This is an anticoagulant, a vitamin K antagonist that is regularly prescribed after an embolic event such as a stroke or a PE. It is also used prophylactically for AF and after the insertion of prosthetic heart valves.

In terms of side effects and contraindications, many of these relate to bleeding. Ether bleeding as part of a disease such as a peptic ulcer or a hemorrhagic stroke, or oxygenicly such as following surgery.

Apart from the obvious risks of causing bleeding, it also has a lot of interactions. This is due to its use of the cytochrome p450 enzyme pathway. Which means it needs to be very careful not only when you prescribe it, but if you're prescribing anything else for a patient who's already taking it.

Always look in the BNF and talk to senior colleagues and pharmacists when prescribing with or for Warfarin.

It's worth briefly talking about the interactions in the cytochrome p450 pathway. A key distinction to make is between those drugs that induce versus those drugs that inhibit it.

Induces induce the enzyme activity, thus decreasing Warren's concentration, which, in turn, decreases INR. This will increase the chances of a thrombus.

Inhibitors inhibit the enzyme that breaks down warfarin and, thus, causes more of it to remain in the bloodstream. This increases INR and decreases the chance of thrombus. But, importantly, may increase the chance of hemorrhage.

Interactions aside, it's more likely that you're going to cause damage by over prescribing anticoagulants and that's causing a hemorrhage, rather than under prescribed increasing the chance of a thrombus.

Similarly, be aware that it can take 48 hours for a single dose to have an effect. So, be careful and increasing the dose too quickly.

Finally, patients in primary care are being moved off Warfarin because of its interactions a narrow therapeutic window on to newer oral anticoagulants such as Dabigatran, Apixaban and Rivaroxaban.


Temazepam is a short-acting benzodiazepine often used for insomnia. This means that the most likely situation you're going to be prescribing it is in the early hours of the morning as an on-call shift for a patient who's unable to sleep.

There's a fair amount of controversy about the use of sedation in hospitals. Some doctors believe that it's appropriate because a hospital environment with interruptions, noise and light is a difficult place to settle in. And it is important for patient to get a restful sleep to aid recovery.

Other doctors feel that it's overused and used is a shortcut to calm agitating patients when other non-medical measures would be more appropriate.

If you do prescribe it, the typical dosage and route is 10 to 20 milligrams PO Nocte.

This sedation is prescribed when the patient is on an existing long-term sedative prescription for insomnia or anxiety. If the admission is prolonged, you can consider trying to gradually reduce the dose and wean the patient off the sedative.

Also it is used if acute anxiety is causing symptoms such as chest pain or bone pain and metastatic malignancy. Although, do be aware to consider that the symptoms might be causing the anxiety rather than the other way around.

Anxieties can be used as pre medication before surgery or other invasive procedures. Although, typically you use a longer acting benzodiazepines such as diazepam.

Sometimes it's required if a patient is agitated and danger to him or herself or others around them. It can also be used to help a patient sleep if nothing else has worked.

You should avoid prescribing sleeping tablets when nothing else has helped, such as milky drinks, low lighting, noise or even a small amount of whiskey.

Also be aware that it's likely to be ineffective at an agitated and wandering patient. It can actually cause confusion, ataxia and even coma in the elderly. especially if they have renal or hepatic impairment. So, make sure that your initial dose is not too high.

Finally, and this is less likely to be an issue in the acute environment, but dependence is a problem. Be aware of the length of time a patient has been on Temazepam. Alternative options might be appropriate.


Morpine or morphine salts is an opiate, a powerful painkiller. Doctors can be a little hesitant to prescribe morphine. But it's important to remember that a primary duty a doctor is to ensure that
patients aren't in pain.

Key things to remember when prescribing morphine is to assess the ability of the patient to metabolize the amount her or she takes. A typical loading dose is 5-10mg IV/IM/SC.

It is important to monitor how the patient responds to these this in terms of how their pain is and also for signs of respiratory depression.

A well as the potentially life-threatening side effect of respiratory depression, there are several other important and common side effects to consider. They include nausea, vomiting in initial stages, constipation and dry mouth. #

Constipation is the most common side effect of chronic opioid use. It should be minimized firstly by making sure the patient is well hydrated and where possible encourage to mobilize. But you are likely also to need to manage it medically with the use of stool softener and a stimulant laxative.

An overdose of opioids needs to be managed with Naloxone. Do be aware that the half-life of Nalaxone is shorter than for morphine and so without careful monitoring it may wear off before the Morphine has and cause the patient to deteriorate again.


Aspirin is used both as an anti-platelet and antipyretic analgesic. It is classed as a non-steroidal anti-inflammatory drug (NSAID). Not only does it have a lot of interactions with other drugs, especially in relation to its antiplatelet activity, but it also has some serious side effects if used in the wrong type of patient.

Aspirin is contraindicated in children under 16 years old unless specifically indicated as it can cause a serious condition called Reye's Syndrome.

It's antiplatelet action means it should be avoided in those with the risk of deranged bleeding, such as haemophilia, previous or active peptic ulcer.

It should be noted that people may also have a hypersensitivity reaction to aspirin. This can be cutaneous, respiratory or a systemic type of reaction. The first two are more common.

Respiratory reactions present within minutes to hours much like an asthma attact. Sometimes with rhinitis, conjunctival irritation and facial flushing.

A cutaneous reaction presents with rhinitis and/or angioedema.

A systemic reaction is rare but far more serious. It causes hypertension, hypotension, laryngeal edema and ultimately loss of consciousness.

In terms of more general side effects these are similar to those found in other NSAIDs such as gastrointestinal irritation, potentially leading to hemorrhage. These can be chronic and asymptomatic. Minimize this by advising the patient to always take their Aspirin with food.

Bronchospasm is another potential side effect, which can be very dangerous and which is why Aspirin should be avoided in asthmatics. Additionally, patients may develop confusion, tinnitus and skin reactions. So, do look out for these although they are rare.

Aspirins a key drug in the management of MI and ACS where 300 milligrams should be given PO. And this should be followed by 75 milligrams PO thereafter as secondary prevention.

It's also used for those suspected of having a TI with an initial dose of 300 milligrams.

Overdose is possible we Aspirin. It typically presents with tinnitus, hyperventilation, tachycardia and metabolic acidosis.

Note that there is no specific antidote available for salicylte. The principles of treatment include stabilizing the patient, limiting absorption, enhancing elimination and correcting any metabolic abnormalities while also providing supportive care.

Be aware that overdoses may be unintentional such as in an elderly person, who has taken more than he or she should over an extended period of time to combat pain.


Methotrexate is an immune suppressant and that is used by many different specialties including oncology, gastroenterology, rheumatology and dermatology to dampen down the immune response.

As you'd expect its biggest effect is on the body, which also means it has a wide range of side effects. There are over fifty listed across all the body systems in the BNF. there are also some absolute contraindications such as pregnancy and breastfeeding.

These adverse effects means that there's a requirements both educate and constantly monitor the patient.

If you're starting a patient on Methotrexate, they will need to have a full blood count and a liver function tests as well as a chest x-ray. Blood tests then need to be repeated every one to two weeks until the therapy is stabilized, after which they should be monitored every two to three months.

It is also important to tell the patient to look out for symptoms of infection or bleeding such as a sore throat, mouth ulcers or bruising, signs of liver toxicity such as nausea, vomiting, abdominal pain or dark urine and respiratory effects, such as shortness of breath.

Finally, the patient needs to know that they should avoid aspirin and other NSAIDs such as Ibuprofen as they affect the body's ability to excrete Methotrexate and thus can cause Methotrexate toxicity.

In terms of dosages and routes, it's an oral medication and comes in 2.5 milligram and 10 milligram tablets. It is important to remember that Methotrexate is almost always only a weekly dosed


Penicillin is a commonly used antibiotic both in primary and secondary care. Despite growing concerns about antibiotic resistance, it's still used regularly and is effective in both primary and secondary care for bacterial infections in all systems.

When prescribing penicillin and other antibiotics it's vital that you follow local guidelines as common types of bacteria and their resistance will vary between regions and even between hospitals.

Penicillin comes in many forms, not all of them with the word penicillin in their name.

Penicillin G or benzylpenicillin sodium must be administered IV or IM while penicillin V (Phenoxymethylpenicillin) can only be administered PO.

There are also resistant penicillin, such as Flucloxacillin, broad-spectrum Penicillin such as a Methicillin and Amoxicillin. And finally, we have Antipseudomonal and Penicillin and Mecillinams.

Penicillin allergy is relatively common affecting between 1 to 10% of people who take it. Although, full anaphylactic reactions are rarer fewer than 0.5% of treated patients.

You should always find out what the patient means by allergic, as reactions can vary from mild, such as a slight rash, to life-threatening.

Also remember that other antibiotics may also contain penicillin.

Finally, other beta-lactams don't contain penicillin, but people allergic to penicillin may also be allergic to these.

As well as the hypersensitivity reactions, another rare but serious toxic effects of the penicillins is encephalopathy due to cerebral irritation.

Finally, diarrhea is a common side effect and you should warn a patient about this.


Corticosteroids like Prednisolone have a wide-ranging immunosuppressive effect on the body and, thus, they have many effects and side effects. Prednisolone specifically has a primarily glucocorticoid function, but it also has some mineralocorticoid function, as well.

With regards to side effects, its glucocorticoid action causes impaired glycemic control, osteoporosis, proximal myopathy, psychoses, gastrointestinal bleeding and Cushing's syndrome.

It's mineralocorticoid adverse effects cause water and the sodium retention, which can lead to hypertension. Additionally, the immunosuppression that occurs can lead to increased infections and persistently raised white cell counts.

For patients who are presenting for surgery, steroid use is very important. The stress of surgery can cause hypotension, at an aesthetic induction and also cardiovascular instability.

Do not forget the patients who've been on steroids for a long period of time, typically more than three weeks at any dose or more than a week at more than 40 milligrams of prednisolone or its equivalent, must be weaned off them slowly or they may suffer an adrenal crisis.

The symptoms to be aware of include hypotension, especially postural hypotension, circulatory collapse, anorexia, nausea and vomiting with severe abdominal pain. Neurological symptoms are also possible such as confusion, which could actually progress to delirium or seizures.

Patients should be given and should carry with them at all times a steroid treatment card if they're on long-term steroids to help minimize this happening.


When poorly prescribed, it can be fatal. That is why it's really important to make sure that it's done carefully.

Insulin is prescribed in units. You should never put insulin on the PRN side of the prescription cards.

If a patient is likely to need a varying dose of insulin you can have a specific prescription chart for it. Don't try to fit it onto a normal one.

There are several pitfalls relating to insulin prescription. One is the widely varying doses that different patients need or even the same patient in different circumstances.

There are also several different formulations of insulin with different lengths of action. They are unusually for drugs often referred to by their brand name rather than their generic name.

All preparations must be given by injection as their inactivated by gastrointestinal enzymes. As a rule, all insulin is given subcutaneously except for a few specific cases.

It's important to tell the patient to rotate the sites used for subcutaneous injection to minimize the chance of localizied lipo dystrophy, which is the loss of subcutaneous fat.

Note, that if a patient is on insulin, you may need to manage this with a sliding scale. There should be detailed guidelines on how to do this at your hospital. Follow them closely and get senior and/or pharmacists support to help you with this.

Remember that when you're using sliding scales with short acting insulins, it can only be given by an IV infusion subcutaneously.

Be aware that insulin induces a net movement of potassium into cells. Hypokalemia can lead to cardiac rhythm problems. So, you need to make sure that you check potassium levels regularly and be ready to supplement patients potassium with a separate IV infusion.

Finally, both real or antibiotic failure will affect the absorption and excretion of insulin and illnesses stress can also change the patient's requirements.

You need to be aware that the patient may need to have different levels of dosage depending on their situation.


Antipsychotics are a large and complex group of medications and it's difficult to name a single one that you're more likely to come across as an f-1.

They all have a lot of side effects, cautions, contraindications and interactions.

Because of their broad action on these different receptors, antipsychotic side effects are common and contributes significantly to non-adherence to therapy. For example, confusion and dizziness in relation to neurological system with extrapyramidal effects caused by the dopamine antagonism.

In the endocrine system many antipsychotics can cause hyperprolactinemia, which can lead to sexual dysfunction.

Many also called high cause hyperglycemia and weight gain. Cardiovascular side effects include tachycardia, arrhythmias due to acute elongation and hypotension. These are very dangerous always check your patient with an ECG.

In terms of side effects, one of the most worrying ones to consider and for which all patients are monitored with at least monthly blood tests is a granulocyte assess resulting in neutropenia. If a patient presents with this you must stop the drug immediately I'm referring to a hematologist.

Additionally, while rare neuroleptics malagant syndrome can not be forgotten as a complication of antipsychotics. This was in the news in summer 2014 when a young Bristol woman died of it because her doctors didn't recognize it.

Associated with these side effects are the relevant diseases. That means you should you antipsychotics with caution. These include cardiovascular disease, Parkinson's disease, epilepsy, depression and myasthenia gravis among others.

Antipsychotics are explicitly contraindicated in comatose states, CNS depression and Phaeochomocytoma. They may also be relatively contraindicated in the elderly, pregnant women and those with renal or hepatic failure.

A list of interactions between antipsychotics and other drugs is far too long to cover off.

Finally, in terms of dosages a useful point to remember is that the IM dose. especially if the patient is agitated, can afford to be less than the dosage that you would have given them PO, as it's not experiencing the first pass effect.


Finally, we have Furosemide also called Frusemide. This is a loop diuretic that inhibits the sodium potassium pump in the ascending loop.

It can be used for edema, especially pulmonar oedema to left ventricular failure, and in resistant hypertension.

In terms of dosage, 40 milligrams would be a typical starting dose and it can go up to 120 milligrams in the case of very resistant edema.

If you're prescribing for pulmonary edema in an acute setting, 18 milligrams IV would be an appropriate start dose.

If you want the patient to take a regular oral dose, you need to be explicit about the times that it should be taken. Ideally, give it as a split dose: first thing in the morning at 8 a.m. and then again soon after lunch 2:00 p.m. It starts to work within an hour of being taken and has finished its action within six hours. Avoid prescribing it in the evenings for obvious reasons.

Furosemide action is on the sodium potassium pump, which can result in an electrolyte reduction in the blood stream. This includes hyponatremia, hypokalemia, hypocalcemia, hyperchloremia and hypomagnesemia. Hypokalemia is the most dangerous due to its effect on the heart.

Additionally, you should look out for hypotension, particularly postural hypotension, and warn the patient that it may lead to gout.

Note that the elderly are particularly susceptible to side effects. New prescription should be started as a low dose and continuing prescriptions should be adjusted according to renal function.

Finally, as a general note regarding diuretics, remember that if somebody has oliguria, it may be tempting to prescribe diuretics, but this is often the last thing you should do. As there may be under perfused and hypovolemic rather than retaining water. Make sure you always know the cause of any oliguria before commencing management.