Doxepin (Sinequan)

How long does doxepin take to work?

• It can take between two to four weeks of taking doxepin before it starts to work, so it's very important that you keep taking it, even if it doesn't seem to make much difference at first. You'll usually need to keep taking doxepin every day for several months, and for at least six months after you feel better. You should keep taking it for as long as your doctor asks you to.

How do I take doxepin?

• You'll usually start on a low dose that is gradually increased. 
• Doxepin is often taken once a day at bedtime because it can make you sleepy. However, your doctor may sometimes ask you to take a smaller dose two or three times a day. 
• Doxepin capsules can be taken either with or without food, on a full or empty stomach.

Doxepin is not addictive. However, do not suddenly stop taking doxepin, because this can cause withdrawal symptoms such as feeling sick, shivering, headache, difficulty sleeping, sweating, irritability, restlessness or anxiety. Withdrawal symptoms are temporary and are not due to dependence on the medicine. They can usually be avoided by stopping doxepin gradually, usually over a period of weeks or months, depending on your individual situation. Follow the instructions given by your doctor when it's time to stop treatment.

What should I know about taking doxepin?

• Doxepin may cause drowsiness, dizziness, problems concentrating and blurred vision and could reduce your ability to drive or operate machinery safely. Do not drive or operate machinery if affected.
• Doxepin can sometimes make you feel dizzy or unsteady when you get up from lying down or sitting, especially when you first start taking the medicine. To avoid this try getting up slowly. If you do feel dizzy, sit or lie down until the symptoms pass.
• Doxepin can cause a dry mouth, which may increase the risk of tooth decay if you take doxepin for long periods of time. It's important to practice good oral hygiene and visit your dentist regularly for check-ups.
• Doxepin may make your skin more sensitive to sunlight than usual. Don't use sunbeds or sunlamps and avoid exposing your skin to excessive amounts of strong sunlight until you know how it affects you.

Can I drink alcohol with doxepin?

• You should avoid drinking alcohol while taking doxepin because it will make you more likely to feel sleepy, dizzy or confused, or to have blurred vision. This effect is likely to be worse if you drink alcohol when you start treatment or after any dose increases.

What are the possible side effects of doxepin?

• Drowsiness.
• Dry mouth.
• Constipation.
• Blurred vision.
• Sweating or flushing.
• Dizziness, particularly when getting up.
• Fast heartbeat.
• Sleep disturbances such as difficulty sleeping or nightmares.
• Feeling confused or disorientated.
• Feeling weak or tired.
• Agitation.
• Pins and needles sensations.
• Headache.
• Hair loss.
• Rashes.
• Increased sensitivity of the skin to sunlight.
• Sexual problems such as reduced sex drive.
• Weight gain.
• Involuntary muscle movements such as tremors or twitching (rare).
• Problems with speech (rare).
• Difficulty passing urine (rare).
• Breast enlargement or production of breast milk (rare).
• Reduced numbers of red blood cells, white blood cells or platelets in the blood (rare). Tell your doctor if you experience a sore throat, high temperature (fever) or unusual bruising or bleeding while taking doxepin, because these could be a sign of a problem with your blood cells.
• Convulsions (rare).

Can I take over-the-counter medicines with doxepin?

• If you need to take a painkiller it's fine to take paracetamol, aspirin or ibuprofen with doxepin, assuming these are appropriate for you. 
• You shouldn't take cold and flu remedies that contain a decongestant such as pseudoephedrine or phenylephrine while you're taking doxepin.
• If you need an antihistamine it's best to avoid those that can make you sleepy, like chlorphenamine, go for a non-sedating one like cetirizine or loratadine instead.

What about prescribed medicines?

You're more likely to feel sleepy on doxepin if you also take other medicines that can cause drowsiness, such as the following:

• antipsychotics, eg haloperidol
• barbiturates, eg phenobarbital, 
• benzodiazepines, eg diazepam,
• sedating antihistamines, eg promethazine, 
• sleeping tablets, eg zopiclone
• strong opioid painkillers, such as morphine, codeine, tramadol, fentanyl
• other tricyclic antidepressants, eg amitriptyline.

You may be more likely to feel dizzy or faint if you take doxepin alongside medicines that lower blood pressure, including medicines used to treat high blood pressure and medicines that can lower blood pressure as a side effect, for example benzodiazepines. If you're taking medicines that lower blood pressure, tell your doctor if you feel dizzy or faint after starting treatment with doxepin, as your doses may need adjusting.

You're more likely to get a dry mouth, constipation, difficulty passing urine or blurred vision if you take medicines that have anticholinergic effects with doxepin. These include the following:

• anticholinergics for urinary incontinence, eg tolterodine, oxybutynin
• anticholinergics for Parkinson's symptoms, eg procyclidine, trihexyphenidyl
• some antihistamines, eg promethazine, chlorphenamine
• antispasmodics, eg hyoscine, atropine
• some antipsychotics, eg chlorpromazine, clozapine
• certain other antidepressants
• some antisickness medicines, eg meclozine, cyclizine.

If you take other medicines or drugs that enhance serotonin activity in the brain while you're taking doxepin, you may be more likely to get a side effect called the 'serotonin syndrome', with symptoms such as agitation, tremor, shivering, increased heart rate and diarrhoea. Other medicines that increase serotonin activity include the following:

• dapoxetine
• dexamfetamine
• fentanyl
• illegal drugs such as cocaine, amphetamine (speed) and ecstasy (MDMA)
• lithium
• linezolid
• methadone
• selegiline, rasagiline or safinamide for Parkinson's
• SSRI, tricyclic or related antidepressants, eg paroxetine, citalopram, amitriptyline, duloxetine, venlafaxine
• tramadol
• triptans for migraine, eg sumatriptan
• tryptophan.
• Doxepin may alter the anti-blood-clotting effect of coumarin anticoagulant medicines such as warfarin. Your doctor may want to check your blood clotting time (INR) more frequently if you are taking these two medicines together.

The following medicines may increase the blood level of doxepin and could increase the risk of its side effects:

• bupropion
• cimetidine
• methylphenidate
• protease inhibitors for HIV such as ritonavir
• SSRI antidepressants such as fluvoxamine and fluoxetine
• terbinafine.

If you get a dry mouth while taking doxepin you may find that medicines that are designed to dissolve and be absorbed from under the tongue, eg sublingual glyceryl trinitrate (GTN) tablets for angina, become less effective. This is because the tablets do not dissolve properly in a dry mouth. To resolve this, drink a mouthful of water before taking sublingual tablets.

Doxepin should not be taken with a monoamine oxidase inhibitor antidepressant (MAOI), eg phenelzine, tranylcypromine, isocarboxazid, or moclobemide. Treatment with doxepin should not be started until at least two weeks after stopping an MAOI and vice versa.

References:

https://medlineplus.gov/druginfo/meds/a617017.html

https://www.netdoctor.co.uk/medicines/antidepressants/a7531/doxepin/

https://www.drugs.com/mtm/doxepin-sinequan.html

https://en.wikipedia.org/wiki/Doxepin

https://www.healthline.com/health/doxepin-oral-capsule

https://www.rxlist.com/consumer_doxepin_silenor/drugs-condition.htm