Dozens of common medications, both prescription and over-the-counter, can make you tired. The most frequent culprits include antihistamines, antidepressants, blood pressure drugs, muscle relaxants, anti-seizure medications, benzodiazepines, and opioid painkillers. Some cause drowsiness as their primary effect, while others produce fatigue as an unwanted side effect you might not expect.
Allergy and Cold Medicines
Antihistamines are one of the most common causes of drug-related drowsiness, and many people take them without realizing how sedating they can be. Older antihistamines like diphenhydramine (the active ingredient in Benadryl and most OTC sleep aids) and doxylamine (found in Unisom and NyQuil) are especially potent. These drugs are fat-soluble, which means they easily cross from your bloodstream into your brain. Once there, they block histamine receptors, occupying more than 50% of them in brain tissue. Histamine is one of the chemicals your brain uses to keep you alert, so shutting it down produces significant sedation.
Newer antihistamines like cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra) were designed to stay mostly outside the brain. They cause far less drowsiness, though cetirizine still makes some people sleepy. If your allergy medicine is knocking you out, switching to a newer option can make a real difference.
The “hangover effect” is worth knowing about too. OTC sleep aids containing diphenhydramine or doxylamine can leave you groggy well into the next day, with dry mouth, constipation, and lingering fatigue on top of it.
Antidepressants
Not all antidepressants affect energy the same way. Some are sedating, others are activating, and the differences can be significant. Mirtazapine is one of the most sedating antidepressants available, partly because it blocks histamine receptors in the brain, similar to how older allergy medicines work. Tricyclic antidepressants like amitriptyline and doxepin also tend to cause considerable drowsiness through this same mechanism.
Among the SSRIs (the most commonly prescribed class of antidepressants), paroxetine causes the most sedation, while fluoxetine (Prozac) leans in the opposite direction, sometimes producing restlessness or activation rather than sleepiness. Trazodone, often prescribed at low doses specifically as a sleep aid, is another antidepressant where sedation is the dominant side effect. If fatigue is dragging you down on one antidepressant, there are often alternatives within the same class that behave differently.
Blood Pressure Medications
Beta-blockers are a well-known source of fatigue that catches many people off guard. Drugs like metoprolol and atenolol don’t just slow your heart rate and lower blood pressure. They also block signals to the pineal gland, a small structure in the brain that produces melatonin, your body’s natural sleep hormone. Because the pineal gland sits outside the brain’s protective barrier, even beta-blockers that don’t easily enter the brain still suppress melatonin production. This disrupts nighttime sleep quality, which then shows up as daytime fatigue. Some patients on beta-blockers have nighttime melatonin levels as low as 10 pg/ml, compared to the typical range of 40 to 100 pg/ml.
Alpha-blockers, another class of blood pressure drug, can also cause drowsiness, particularly when you first start taking them or after a dose increase.
Anti-Seizure Medications
Anticonvulsants work by calming overactive electrical signals in the brain. The trade-off is that this calming effect often extends beyond seizure control and into general sedation. Pregabalin (Lyrica), frequently prescribed for nerve pain and fibromyalgia, causes drowsiness in about 22% of patients, compared to 7% of people taking a placebo. That drowsiness is significant enough that 2 to 3% of patients stop taking the drug because of it. Gabapentin, a closely related medication, carries similar risks.
These drugs dampen excitatory activity in the nervous system. That’s what makes them effective for seizures and nerve pain, but it also means fatigue is baked into how they work rather than being a rare or unpredictable reaction.
Muscle Relaxants
Muscle relaxants are among the most sedating medications prescribed for everyday conditions like back pain and muscle spasms. Cyclobenzaprine is structurally similar to tricyclic antidepressants and produces the same kind of heavy lethargy and dry mouth. Tizanidine causes drowsiness, fatigue, and dizziness as its most common side effects, though its short half-life of roughly 2 to 4 hours means the sedation wears off relatively quickly compared to some alternatives. Diazepam (Valium), sometimes used as a muscle relaxant, is a long-acting benzodiazepine that adds sedative, anti-anxiety, and hypnotic effects on top of muscle relaxation.
If sedation is a problem, methocarbamol and metaxalone are generally less sedating alternatives that your prescriber might consider. The sedation from muscle relaxants also stacks with other sedating drugs. Taking tizanidine alongside a benzodiazepine, opioid, or sedating antidepressant can produce dangerously excessive drowsiness.
Benzodiazepines and Sedatives
Benzodiazepines like alprazolam (Xanax), lorazepam (Ativan), and clonazepam (Klonopin) work by boosting the activity of GABA, the brain’s primary “slow down” chemical. This is what makes them effective for anxiety and insomnia, but it also makes tiredness their most predictable side effect. Longer-acting benzodiazepines can cause grogginess that persists well into the following day, while shorter-acting ones wear off faster but may cause more noticeable rebound effects.
Opioid Pain Medications
Prescription opioids like oxycodone, hydrocodone, and morphine suppress activity throughout the central nervous system, producing sedation alongside pain relief. This drowsiness is typically strongest when you first start the medication or after a dose increase, and it may lessen somewhat over time as your body adjusts. However, for many people the fatigue never fully goes away, particularly at higher doses.
Cholesterol-Lowering Statins
Statins are not typically thought of as sedating medications, but fatigue is more common than many people realize. In a large registry of statin users, 14% of current users and 20% of former users reported fatigue as a symptom. Muscle aches and weakness, which are better-known statin side effects, often accompany this fatigue. The tiredness from statins tends to feel more like general physical exhaustion than the mental drowsiness caused by antihistamines or sedatives.
Why These Drugs Make You Tired
Medication-induced fatigue generally works through one of two pathways. Some drugs reduce excitatory activity in the brain, essentially turning down the signals that keep you alert. Anticonvulsants and certain blood pressure drugs work this way. Other drugs increase inhibitory activity, amplifying the brain’s natural braking system. Benzodiazepines and barbiturates fall into this category, boosting GABA signaling so your nervous system runs at a slower pace. Antihistamines take a third route, blocking the histamine system that your brain relies on to maintain wakefulness.
Many sedating medications affect more than one of these pathways simultaneously, which is why combining them is particularly risky. Two mildly sedating drugs taken together can produce severe drowsiness that neither would cause alone.
Managing Medication-Related Fatigue
Timing your dose can help. Taking a sedating medication at bedtime instead of in the morning lets you sleep through the peak drowsiness and wake up after the worst of it has passed. This works especially well for drugs with shorter half-lives that clear your system within a few hours.
Fatigue from many medications is strongest in the first few weeks and gradually improves as your body adjusts. If the tiredness persists beyond that initial period, your prescriber may be able to lower the dose, switch you to a less sedating alternative within the same drug class, or adjust the timing. Stopping a sedating medication on your own can cause withdrawal symptoms or allow the condition it’s treating to flare, so any changes should be coordinated with whoever prescribed it.
It also helps to look at the full picture of everything you’re taking. A single mildly sedating drug might be tolerable, but adding a second or third, including OTC products like nighttime cold medicines or sleep aids, can push the combined effect into territory that makes it hard to function during the day.