The song "Express Yourself" was released in response to the backlash against "Fuk tha Police", which had been banned from the radio along with several other songs. The song, as it's title suggests, is about a rappers right to express themselves. I believe Dr. Dre is being ironic when he says he doesn't smoke weed. If you listen to other raps by the group such as "Straight Outta Compton" the group states that they use the drug, "Since I was a youth I smoked weed out...". So, I'd say his views didn't change. He was instead ironically imitating non-controversial rap groups such as Run DMC who had anti-drug messages, because they were the ones who were allowed on the radio. Throughout the song no profanities are used. They are making a satire of the kind of raps the radio stations allowed, because they aren't able to truly express themselves.

White, Miles. "Real Niggas: Black Men, Hard Men, and the Rise of Gangsta Culture." From Jim Crow to Jay-Z Race, Rap, and the Performance of Masculinity.

Edit: The song was not a specific reaction to the retaliation over "Fuk That Police" since both songs were dropped at the same time on the album "Straight Outta Compton", Tracklist. The song was in fact a satirical response to other rappers and their submission censorship at the time. See above references. - Thank you to /u/GaryTheJerk.

I don't know if it is OK to do this here, but I wanted to refute the implicit point that this discussion isn't important that has sprang up a few times in the thread, most of which seems to have been cleaned up.

Rap culture is a really important lens to view the mid to late 1980's and 1990's in American history but is still important today. Here is an essay posted on Standaford University's website about the subject and here is a class Yale teaches on the subject.

Basically, rap music was an outlet for African Americans when a lot of that community felt like they had no outlet. A kind of cynicism about the success of the civil rights movement, and the lack of real tangible change for poor blacks, sets the tone for much of what NWA rapped about. Pot culture is another salient point pioneered by rappers as well that is a major political conflict today. The ability to sell pot and other drugs was the only real means of income for a lot of poor blacks and the culture that came out of that, as derided as it is in a lot of circles, has become very powerful and very popular in its wake.

You can also use rap to see the shifting change in cultural focus, from having a discussion about systemic oppression and a general shift towards getting rich and achieving the American dream of cars, sex, and luxury.

So in my opinion this discussion belongs here because even though rap is something in our very recent history it is an important part of it and tells us a lot about where we are today.

To answer the question more directly, as others have done better, it would seem that Dr. Dre has been pretty vocal his entire career in marijuana use, despite what he said in Express Yourself. In an interview with GQ he said:

"So you actually smoked “the chronic,” that particular strain of weed?
Yeah.

You didn’t freak out the first time?
Nah. I liked it.

Did it become part of your creative
process?
Weed doesn’t make me more creative. I don’t smoke before I work. I like to smoke when I’m done and listen back to the music, under the influence. [laughs] Some people can go in and smoke from morning to evening and it doesn’t affect them. But it slows me down. I’ve definitely created stuff high before, but I prefer to do it the other way.

When was your peak of weed smoking?
Um—last night? [laughs] It’s still goin’. Nothing’s changed."

I cannot actually ascertain the date of the interview, but it would seem that he still smokes weed as many rappers do.

Edit: Cleaned up some stuff

When Eazy-E was beefing with Dr. Dre after Dre left Ruthless Records, he released an EP called It's On Dr.Dre 187^um Killa. He took a couple shots at what he saw as Dr. Dre's hypocrisy about weed on this album.

On the song "It's On" (which parodies "Nuthin' But A G Thang" he says "Smoke a little sherm now you call that shit the chronic"

And he sampled the line that you're talking about from "Express Yourself" on his song "Down To Tha Last Roach" (and then proceeded to call Dr. Dre a bitch.)

Similar question, what was the reaction to Eazy-E's death from other NWA members?

From what I remember from my popular culture and music class theres a general belief that the song express yourself was supposed to be a commentary on those who "sold out" in rap. First off Dre uses the line "meditate like a Buddha" very early in the song that is a phrase used to describe smoking weed. Considering how the lyrics were written a lot of the times by Ice Cube and Ren (who smoked) they both were probably making a commentary on the push in the 90s and 80s towards villianizing drugs with false rhetoric. This idea of commentary on the current state of rap is furthered when Dre says lines like "Forget about the ghetto and rap for the pop charts Some musicians curse at home But scared to use profanity when up on the microphone". The thing about this song is that it is one of the groups only really "clean" songs hence why the music video was first shown on MTV and allowed them to gain a larger audience. In my opinion, I think this song did have a strong message about how people viewed rap or at least wanted rap to act but Dre was trying to say that he didn't care because NWA was going to express themselves. The rest of their music is considered much more "controversial" that this song sticks out like a sore thumb because it was supposed to be so widely different. TDLR: The song is a commentary on the state of the rap industry and really doesn't suggest that Dre didn't smoke weed.