Common and Severe Medication Side Effects, Adverse Effects, and Allergies

Adverse effect

An unintended or undesired effect of a drug.

Types: allergies, gastrointestinal effects (e.g., nausea, vomiting, diarrhea, abdominal pain), central nervous system (CNS) effects (drug dependence, tolerance, drowsiness), hematological effects (blood clotting, bleeding), nephrotoxicity (kidney[renal] impairment), hepatotoxicity (liver impairment), ototoxicity (causes damage to the ear), immunosuppression (reduces the ability to fight infection), carcinogenicity (ability to cause cancer), and teratogenicity (the ability to harm the fetus or cause birth defects in pregnant women).

Side effect

An unintended secondary effect of a medication.

Allergy

It occurs when the body’s own immune system reacts to the presence of a foreign substance (e.g., a drug) and causes an adverse effect.

Anaphylactic shock

A life-threatening reaction that results from dangerously low blood pressure and shortness of breath. Anaphylaxis should be treated immediately with epinephrine (e.g., EpiPen).

Statins

The most common class of antihyperlipidemic medications is the HMG CoA reductase inhibitors, which is another name for these types of medications.

The side effects of these medications are: headache, nausea, abdominal pain, drowsiness, dizziness, and muscle aches. Some patients may experience more serious muscle side effects called myopathy or rhabdomyolysis

Beta and alpha blockers

They commonly cause fatigue (tiredness), cold hands, upset stomach, constipation, dizziness, shortness of breath, low blood pressure (hypotension), low heart rate (bradycardia), and fainting.

Calcium Channel Blockers

They can cause adverse effects such as dizziness, swelling, blurred vision, fatigue, and weight gain.

ACE Inhibitors

They are known for causing an unproductive dry cough, high potassium levels (hyperkalemia), nausea, and loss of appetite.

Diuretics

They can lead to adverse effects such as dry mouth, weakness, loss of appetite, muscle twitching, upset stomach, and electrolyte imbalances.

Antibiotics

They are used to treat bacterial or microbial infections. These types of medications have the potential to cause nausea, vomiting, diarrhea, stomach upset, and abdominal pain. They can also kill the normal flora (good bacteria) in the body and lead to secondary infections, such as thrush or intestinal infection (colitis, Clostridioides difficile).

Penicillins

Side effects

Allergy in 1–10% of patients.
Anaphylaxis (a rare but serious form of allergy).
Skin rash (a common, less severe form of allergy).

Examples: Amoxicillin, Penicillin

Cephalosporins

Side effects

Allergy: About 10% of patients with a penicillin allergy are also allergic to cephalosporins.

Examples: Cefaclor, cefixime

Tetracyclines

Side effects

Sensitivity to sunlight.
Tooth staining, so avoid in children.

Examples: Tetracycline, doxycycline, minocycline

Macrolides

Side effects:

Arrhythmias.
Ototoxicity (ear problems) with high doses.

Examples: Erythromycin, clarithromycin

Quinolones

Side effects

Arrhythmias.
Tendon rupture.
Increased seizure risk.

Examples: Ciprofloxacin, levofloxacin

Sulfonamides (sulfa drugs)

Side effects

Allergy — anaphylaxis or skin rash

Examples: Sulfamethoxazole-trimethoprim (Bactrim)

Antineoplastic agents

They have the same classic chemotherapy side effects. These include hair loss, increased risk of infection (immunosuppression), low red blood cell count (anemia), bruising or bleeding easily, skin rashes (especially at the site of injection), fatigue, nausea, vomiting, diarrhea, constipation, gastrointestinal ulcers, mouth sores, and weight loss. Most of these side effects are due to the fact that they are so good at killing cells that they kill normal body cells in addition to cancer cells.

Metformin

a first-line drug for treating type 2 diabetes mellitus because it has fewer side effects than many of the other antihyperglycemic drugs. It commonly causes nausea and stomach pains, but it does not cause hypoglycemia (too-low blood sugar) or weight gain like many other agents.

Sulfonylureas

very effective at lowering blood glucose and are commonly used as an addition to metformin. However, they are associated with an increased risk of hypoglycemia and weight gain.

Thiazolidinediones

no longer commonly used because they were found to be associated with an increased risk of cardiovascular disease and heart failure. They also cause weight gain and edema (swelling).

Acarbose

rarely used because it often causes abdominal discomfort.

DPP-4 inhibitors

well tolerated by patients and have few side effects. They do not cause weight gain or hypoglycemia like many of the other antidiabetic medications, but they are newer and more expensive.

SGLT-2 inhibitors

They are becoming popular because instead of causing weight gain, they can help diabetic patients lose weight. This is beneficial to diabetics because they are already susceptible to weight gain. Unfortunately, they do increase the risk of genital and urinary tract infections.

Dopaminergic drugs

For PD. They commonly cause nausea, vomiting, agitation, confusion, depression, psychosis, dyskinesias (involuntary muscle movements), compulsive disorders (e.g., gambling), and orthostatic hypotension (dizziness upon standing).

MAO-B inhibitors

For PD. They also cause a number of adverse effects that are similar to those of dopaminergic drugs. The common side effects for MAO-B inhibitors include nausea, vomiting, agitation, confusion, dizziness, dyskinesias, insomnia, lack of appetite, depression, anxiety, and psychosis.

Anticholinergic drugs

They are used for PD and cause adverse effects similar to those of other anticholinergics that are used to treat urinary retention. Anticholinergic side effects include dry mouth, blurred vision, constipation, urinary retention, confusion, agitation, and psychosis.

Cholinesterase inhibitors

For AD. They have an opposite effect to that of anticholinergic drugs. They increase acetylcholine levels by blocking the enzyme acetylcholinesterase, which is responsible for breaking down acetylcholine. Common side effects include nausea, vomiting, upset stomach, and weight loss.

NMDA receptor antagonists (blockers)

Used to treat moderate to severe cases of AD. NMDA blockers commonly cause dizziness, headache, drowsiness, high blood pressure, and restlessness.

Attention-deficit/hyperactivity disorder (ADHD)

Treated using stimulants such as amphetamines, that excite the brain and help with focus, concentration, and motivation. Common side effects of stimulants include restlessness, nervousness, insomnia, mood swings, raised blood pressure, loss of appetite, stomachaches, headaches, and weight loss.

Opioids

They are central nervous system (CNS) depressants used to treat pain. One of the main adverse effects is a high risk of dependence and addiction, and there are many widely seen advertisements warning of the potentially addictive properties. They can also cause nausea and vomiting in many patients. They also commonly cause constipation. Also, they slow down the movement of the digestive tract, slow down breathing or respiration, and can lead to reduced bowel movements.

Beta agonists

can cause tachycardia (a fast heart rate), cardiac arrhythmias, and tremors. They are also known to cause hypokalemia (low potassium levels). Examples include albuterol, levalbuterol, terbutaline, salmeterol, and formoterol.

Muscarinic antagonists

They are selective and act locally, so they rarely cause significant adverse effects. However, they can potentially cause dry mouth, blurred vision, difficulty urinating, and glaucoma. The patient’s eyes should be protected when administering nebulizers. Examples include ipratropium and tiotropium.

Inhaled corticosteroids

They provide localized actions, so they do not cause as many adverse effects as oral steroids. However, they still have the potential to cause fluid retention, weight gain, hyperglycemia (high blood glucose), and hypokalemia (low potassium). Because corticosteroids reduce the body’s immune response, patients frequently get a localized infection called thrush, a fungal infection in the mouth or throat.

Calcium and Vitamin D supplements

The adverse effects associated with these are uncommon. In rare cases, they can cause hypercalcemia (high blood calcium levels). Signs of hypercalcemia include nausea, vomiting, and thirst. High doses of vitamin D are contraindicated in pregnancy.

Bisphosphonates

used to treat osteoporosis include alendronate (Fosamax), risedronate (Actonel), and zoledronate (Reclast). The main side effects include hypocalcemia (low blood calcium levels) and gastrointestinal ulceration. These medications irritate the esophagus, so they should be taken with a full glass of water and the patient should not lie down for at least 30 minutes after taking the medication in order to avoid irritation to the esophagus.