Side Effects. Drug information provided by: IBM Micromedex. Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. How long do Amitriptyline withdrawal symptoms last? There’s no telling exactly how long Amitriptyline withdrawal will last. For some people who were on a low dose for a short-duration, it may only take a few weeks before they feel 100% back to normal. It is one of its side effects. My mother has be on it for several years and has changed 4 sizes. You can find this side effect on wiki. My mother has be on it for several years and has changed 4 sizes. Some of the long-term side effects of amitriptyline have to do with its effects on the nervous system. For example, amitriptyline can cause nervousness, insomnia, and anxiety in some patients because it can stimulate the nervous system. When drug side effects last a long time some physicians deny they could be caused by the medicine. Tardive Dyskinesia is a Classic Complication: One disturbing irreversible drug reaction is called tardive dyskinesia (TD). Do not use amitriptyline if you have used a MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine. Hi Kelly, if the nausea is a side effect of Amitriptyline it can take 3 to 6 weeks to even out. Most drugs take up to 6 weeks to settle down in your system. My Mom had trouble sleeping last night so my Dad gave her Amitriptyline to calm her nerves down. It did work really good and she slept for the whole night. If you do have side-effects, it's often worth continuing the treatment as they'll usually lessen with time. But if you have any unusual side-effects or symptoms that concern you, see your doctor immediately. The combination of withdrawal symptoms and possible lingering side effects may leave you confused, wondering how long it really takes to clear amitriptyline from systemic circulation. To determine how long amitriptyline is likely to stay in your system, it is necessary to examine its elimination half-life. The elimination half-life of amitriptyline is reportedly within the range of 10 to 50.