Amphetamines are thought to block the reuptake of dopamine and norepinephrine. This theoretically leaves more of these neurotransmitters available in the brain. However if you have low neurotransmitters to start with medications either will not work well or work for a while then stop working.
The precursors that go into the methylation cycle for SAMe, neurotransmitters, dopamine, serotonin are methionine, folate, B12, B6, TMG (trimethylglycine) and zinc, and maybe calcium and magnesium.
This isn't a lot of info online about norepinephrine but Nutritional Healing has this on dopamine deficiency...
"Dopamine deficiency signs/symptoms:
Reduced ability to feel pleasure
Flat, bored, apathetic and low enthusiasm
Low drive and motivation
Difficulty getting through a task even when interesting
Difficulty paying attention and concentrating
Slowed thinking and/or slow to learn new ideas
Crave uppers (e.g. caffeine/nicotine/diet soft drinks)
Use these to improve energy/motivation/mood
Prone to addictions (e.g. alcohol)/addictive personality
Low libido or impotence
Mentally fatigued easily and physically fatigued easily
Sleep too much and trouble getting out of bed
Put on weight easily
Family history of alcoholism/ADD/ADHD
Dopamine levels may be low due to a combination of genetic and acquired reasons. Dopamine can be raised effectively using either nutrient based therapies or medications. Dopamine is synthesized form the amino acid tyrosine.
Factors which reduce dopamine levels:
Lead, arsenic and cadmium exposure
Tyrosine (precursor) deficiency
Magnesium, iron, zinc & vitamins B3/B6/C/D deficiency
Excess copper levels
Genetic dopamine receptor abnormalities
Chronic opioid, alcohol & marijuana use
Human growth hormone deficiency"
You should talk to your doctor about getting some simple blood tests done to confirm/rule out a thyroid disorder.
The tests you need are Free T3, Free T4 and TSH. These will tell you whether or not you have adequate thyroid hormones. You should also get tested for thyroid antibodies, Thyroid Peroxidase Antibodies (TPOab) and Thyroglobulin Antibodies (TPOab); these will tell if you have Hashimoto's Thyroiditis, which is an autoimmune disease that attacks the thyroid. If you have symptoms of hyperthyroidism, such as weight loss, rapid heart rate, palpitations, etc you should also get Thyroid Stimulating Immunoglobulins (TSI) to confirm/rule out Graves Disease, which is another autoimmune disease that attacks the thyroid.
You should also get vitamin B12 tested, as B12 deficiency can cause horrendous fatigue, as well as tingling/numbness in the hands/feet, easy bruising, etc.
Forgot to mention that we're not doctors. We're all fellow patients, trying to help others who are going through what we've gone through.
If you want a doctor's opinion, you can post on the expert forum.