With prolonged use of stimulants (like 4-Fluoroamphetamine) it can lead to psychotic behavior without proper sleep. I wouldn't be surprised if he'd become more manic, a lot more demanding and quick to anger and lacking in inhibition; the latter would be a side-effect of the phenazepam, a benzodiazepine (currently legal?) in the UK, which has been known to cause horrendous blackouts and amnesia.
The 4-AF may cause alertness, lack of appetite, inability to fall asleep (like a couple of cans of 'Red Bull', I suppose...) and various other side-effects one would expect from a stimulant. Here's a list from "Drugs.com" regarding Amphetamines, and since 4-AF is probably similar, I'll just post this, although I expect the effects (both positive and negitive) would be far, far less powerful in the case of a new "Designer Drug"; the most effective drugs tend to be the ones that've been made illegal, thus pushing people to move onto more and more dangerous compounds with far more side-effects...
Constipation; diarrhea; dizziness; dry mouth; headache; loss of appetite; nausea; nervousness; restlessness; stomach pain or upset; trouble sleeping; unpleasant taste; vomiting; weakness; weight loss.
Seek medical attention right away if any of these SEVERE side effects occur when using Amphetamine/Dextroamphetamine:
Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); blurred vision or other vision problems; change in sexual ability or desire; chest pain; confusion; fainting; fast or irregular heartbeat; fever, chills, or sore throat; new or worsening mental or mood problems (eg, aggression, agitation, anxiety, delusions, depression, hallucination, hostility); numbness or tingling of an arm or leg; one-sided weakness; painful or frequent urination; red, swollen, peeling, or blistered skin; seizures; severe or persistent headache; severe stomach pain; severe weight loss; shortness of breath; sudden, severe dizziness or vomiting; slurred speech; uncontrolled muscle movement; unusual weakness or tiredness.
Side-effects might include:
Glassy eyes, much like when you're drunk.
Drunken gait; bad posture, as if standing up is difficult in and of itself.
Slurred speech.
Unexpected and sudden outbursts - you're incapable of feeling anxiety, paranoia or fear and you've (currently) no inhibitions; you're going to say what's on your mind!
Amnesia; deterioration of short-term and eventually long-term memory.
Difficulty forming new memories.
Muscle relaxation, but I suppose that's covered in the bit about gait, posture and speech...
That's just a list of Phenazepam side-effects, by the way. It's a sedative a lot like VALIUM, if you've ever heard of or used a drug similar to it. If not, perhaps a barbiturate or anything like that? Well, phenazepam is not innately dangerous on its own, but when combined with other sedatives that depress the Central Nervous System and slow down one's breathing (alcohol, opiates [morphine, codeine, methadone, diamorphine, etc], barbiturates and literally any other sedative) someone could very well end up dead. However, that'd be an extreme case and I only mention it to warn you...
How long has he been taking these medications without the supervision of a GP, psychologist or doctor of some kind?
Benzodiazepines don't really allow for a lot of REM sleep, so you're not likely to feel as well-rested once you wake up. After seven years on diazepam, I know that I didn't once dream whilst under a heavy dose and I made a lot of spontaneous, dangerously impulsive decisions, with the danger increased when money was involved.
Anyway, enough of my experience. I hope that your son has not been taking this combination for very long, as it's entirely possible to become physically dependent upon both substances, although benzodiazepine withdrawal is a hell you cannot imagine, and amphetamine addiction is typically considered more psychological in nature, though it could also be considered a hell you can't imagine!
[Note: Very tired and typing this with my eyes half-closed. Hope I got some info. correct, but please don't be too harsh on your son. I know it's not my business, but whether we drink, smoke or shoot coke into the veins beneath our tongues, we all end up doing drugs at some point, though I would suggest trying to make sure he keeps it occasional rather than too frequently, as that's when dependency comes in... >_< ]