Yes it's absolutely illegal, about 10 yrs ago I had never been in any trouble at all other then 9mph over the speed limit when I was 18 and I got pulled over on my way home from work and had one of my med bottles and had 2 of each, Adderall,Xanax,perks 1 ambein 1 Viagra and 1 Cialis in the same bottle. Thing is my line of work it's hard to carry a bunch of bottles around full of meds and I had been doing this for 10+ yrs and honestly since they were all prescribed to me had no clue I was breaking the law. I had my bottle stolen out of my truck multiple times so I'd just take x amount in one bottle and before u ask no didn't need the Viagra or Cialis at work lol but they was put in there as a just to have Incase I didn't end up at home that night type of thing. I was charged with 7 felonys and arrested and given a 90,000 bond. Long long story short since I took proof that everything on me was prescribed to me it all got dropped except illegal transportation and even tho it was all dropped I spent almost 10,000 to get out of jail and another 5 on a lawyer and in the end other then rapped of money got a pop on the wrist so no never take any prescription pill in a car unless in the original bottle or hide very well lol. I had mine in the seat and honestly never for all those yrs had a clue I was breaking any laws