Why do only amphetamines make her happy?
Both amphetamines and opiates have been used to treat depression at one time or another. Amphetamines are still used sometimes to augment other medications in severe treatment-resistant depression. Opiates also have a history of use as antidepressants and there have been a scattering of trials over the last 20 years. It’s also been suggested that some forms of depression may be due to dysfunction of the endorphine rather than the serotonin system and that some proportion of functioning addicts are self-medicating their depression rather effectively. But feeling good when you take drugs that make people feel good isn’t an indicator of anything much. So yeah, next step should be to see a doctor.