How does nicotine affect dopamine levels in the brain?

Nicotine increases the activity of dopamine receptors in the brain much more directly than substances like alcohol. This increase in dopamine activity causes a feeling of pleasure that leads to addiction, with an addictive potential equivalent to methamphetamine.

What is the role of phenylalanine in smoking cessation?

Phenylalanine is an amino acid that serves as a chemical bio-precursor to dopamine. During smoking cessation, it helps replace the dopamine deficit that causes withdrawal symptoms like psychological distress and physical tremors, thereby reducing the urge to return to smoking.

Why do individuals with ADHD have a higher tendency to smoke?

Children and individuals with ADHD often have a lack of dopamine. They have a stronger tendency to smoke as a way to compensate for this deficiency, using nicotine to stimulate dopamine activity in the brain.

Nicotine addiction

In psychiatry, nicotine addiction is also considered a psychiatric diagnosis of substance dependence syndrome.
Nicotine increases the activity of dopamine receptors in the brain. All addictive substances increase the activity of dopamine receptors, causing a feeling of pleasure that leads to addiction (some substances, e.g., psychiatric drugs, can increase dopamine levels without causing addiction). In psychiatry, nicotine is considered the strongest drug – its addictive potential is equivalent to that of methamphetamine. The differences between nicotine and methamphetamine are perhaps the possibility of a high single dose and the social consequences.
Nicotine, unlike, for example, alcohol or heroin, increases the activity of dopamine receptors much more directly.
Smoking tobacco, due to its ability to increase dopamine levels, also has great benefits. But that doesn't mean we have to increase our dopamine levels in such an addictive and harmful way.
Children with ADHD have a much stronger tendency to smoke because they need to compensate for the lack of dopamine in this way.

How to quit smoking/get rid of nicotine addiction?
The guide is not a guarantee of how to get rid of addiction. It can only help – first and foremost, the addict's strong, firm, determined will to stop smoking is needed.
When smoking, the body becomes unaccustomed to producing sufficient amounts of dopamine without the support of nicotine. This results in very unpleasant psychological (e.g., feeling unable to think) and physical (e.g., trembling hands) conditions when quitting smoking.
The lack of dopamine needs to be replaced, preferably with a stimulant. A stimulant is a name for a psychiatric type of drug that increases dopamine levels. These substances have the active substance with the chemical structure of methamphetamine.
Importantly, the effect of the stimulant can be replaced by the over-the-counter nutritional supplement phenylalanine, which can be purchased at a pharmacy. Since phenylalanine is also a natural substance in the body, it does not need to be registered as a medicine on the pharmaceutical market; it is sufficient for it to be classified as a "nutritional supplement".
Phenylalanine is an amino acid that is a chemical bio-precursor of dopamine, meaning that dopamine is later chemically formed/synthesized from this substance in the body.
Phenylalanine or a stimulant, in addition to withdrawal symptoms, will reduce the urge to return to smoking.

This is another psychiatric use/indication of phenylalanine:
-The use of phenylalanine is also a preventive way to reduce the likelihood of drug addiction in young people. It reduces the urge to take drugs.
-Improved thinking, higher school performance , easier memorization, faster calculation of mathematical examples or computer programming, higher performance in exams, better perception.
– Treatment of ADHD , attention deficit hyperactivity disorder
-Treatment of depression

https://en.wikipedia.org/wiki/Phenylalanine
http://www.kompava.sk/p/vyzivovy-doplnok-dlpa-extra