Firstly Ritalin and Concerta (among others) are the same drug, methylphenidate. Technically methylphenidate is NOT an amphetamine but it is a powerful stimulant and can cause similar problems. Adderall is a mix of amphetamine and dextroamphetamine and Vyvanse (lisdexamfetamine) is a pro drug meaning it is inactive but breaks down into dextroamphetamine.

Also dose equivalents vary significantly between drugs.
Here is a list of stimulants, the largest dose made and the maximum daily dose. Also keep in mind that doctors can prescribed larger doses. This is primarily done for people with sleeping disorders. For example I have scene 120 mg of Adderall or Dexedrine prescribed (very rare) but even a dose up to 90 mg/day is not unheard of. These doses are also used under careful medical supervision.

Vyvanse (lisdexamfetamine) largest dose is 70 mg
Dexedrine 10 mg is the largest 60 mg/day is maximum
Desoxyn 5 mg is the largest and 25 mg/day is the maximum
Adderall 30 mg is the largest and 60 mg/day is the maximum.
Concerta (methylphenidate controlled-release) largest is 54 mg the maximum daily dose is 72 mg.
Ritlain (methylphenidate) largest is 20 mg the maximum daily dose is 60 mg
Focalin (dexmethylphenidate) 10 mg is the largest dose and the maximum is 20 mg/day.

Physical dangers of amphetamine and methylphenidate abuse:

Cardiovascular collapse (sudden loss of blood flow due to heart), myocardial infarction (heart attack), stroke, seizures (gran mal, status epilepticus), ischemic colitis (swelling of the colon), hepatotoxicity (kidney damage or failure), subarachnoid and intracranial hemorrhage (brain bleed), may result in death. It has been proven that risk of myocardial infarction greatly increases with amphetamine abuse, particularly for those under 45.

Your friend is also underweight, his body mass index (BMI) is 17.6, a normal weight is 18.5- 24.9 anything under is too low. Continued amphetamine abuse will likely cause more weight loss and even vitamin deficiencies and malnutrition.

Amphetamine withdrawal is consistent with the symptoms of a major depressive episode, typically lasting less then two weeks and involving decreased energy, increased appetite, craving for sleep, hypersomnia (sleeping 10+ hrs/day) dysphoria, anhedonia (inability to experience pleasure), and suicidal ideation. Suicide is more common in people abusing amphetamines either during intoxication and especially during the “crash.”

Psychosis, delirium, mood symptoms, obsessive behaviours, repetitive movements, loss of inhibitions, anxiety, insomnia, memory impairment, increase sexual arousal and disinhibition (potentially increasing the risk of exposure to STD’s and inappropriate sexual contact) and oddly enough sexual dysfunction are common in amphetamine abuse.

Amphetamines are neurotoxic when abused, as a result brain damage can occur, number of brain cells and density of brain cells can be greatly reduced. This can lead to irreversible cognitive impairment and severe depression. Toxic-psychosis which resembles schizophrenia can occur, some amphetamines users develop chronic psychosis. Amphetamines are cardiotoxic due to the damage they can do to the heart. Although rare the heart can actually “blow up,” people may also have severe hypertension (high blood pressure) and hyperthermia (fever).

Basically abusing stimulants or alcohol cause the most damage of any drug. Heroin, for example, will not degrade and severely damage the body although injecting drugs and secondary complications can. And damage due to amphetamines may be irreversible.

Since you friend is young his body is more able to repair its self and is better able to adapt. However he certainly could develop amphetamine addiction (although he might already have it). Addicts are unable to stop so he could go on abusing these drugs. If he continues to escalate use of the drugs he may start using street drugs, especially methamphetamine.

If he continues he certainly is putting himself in great danger.