You may have heard that driving while addicted to drugs is a form of DUI in California. This is correct: Vehicle Code 23152(c) VC, a subsection of California's DUI law, criminalizes addicted driving.
VC 23152(c) driving while addicted is a completely separate crime from Vehicle Code 23152(e) driving while under the influence of drugs. You can be guilty of the former even if you never drive while actually under the influence of a drug.
If you are suffering from drug addiction, you may be considering entering a drug treatment program. One potential problem is that doing so is more or less an admission that you are addicted. Does this mean that you can be arrested at any time for driving your car?
Fortunately, the answer is no. California's driving while addicted to a drug law specifically clarifies that it does not apply to people enrolled in approved drug treatment programs. So you can drive freely while enrolled in such a program without worrying about getting a DUI (as long as you do not actually drive under the influence).