There is nothing scarier for a parent than to see your child regress on a supplement. This is similar to parents going on a gluten/casein free, or low oxalate diet and seeing a deterioration in behaviour initially, during the withdrawal period, before their child begins to improve.
This is certainly not a complete list and I will be progressively updating the list as time allows.
Use ARI’s database to find possible treatments for your child.
Please consult a practitioner familiar with supplementing ASD children. There are appropriate dosages that need to be determined, or co-factors than may need to be added. Some children may regress on a supplement, an experienced practitioner will know whether this is transient or a negative reaction to the supplement.