How good a diet pill is dexedrine (dextroamphetamine)?

Not very: Dexedrine (dextroamphetamine) was popular years ago as a diet pill, and it certainly can suppress appetite in the short term for most people. However, that effect tends to wear off over time, so either appetite returns or the dose gets raised, eventually to levels that are dangerous. When you stop the medication, the effect goes away, so regaining weight is the usual result.

Dexedrine: There was a time in this country when amphetamines were often used as diet pills. Actually for decades there was an amphetamine craze when it was used for many different conditions. Dexedrine can be very addictive & has dangerous side effects. Don't recommend it as a weight loss product.