Fentanyl issues could derail the prospects of a U.S.-China trade deal if the Chinese government does not crack down on the highly-addictive pain reliever in good faith, CNBC's Jim Cramer said Monday.

"We may eventually get a trade deal, but it won't be quick, it won't be easy, and you certainly shouldn't be buying stocks just because you think a we're on the verge of some kind of breakout," the "Mad Money" host said.

The world's two largest economies are far from reaching an agreement in part because China has not stopped the inflow of fentanyl, a synthetic opioid, into the United States, Cramer said. It has contributed to the ongoing opioid epidemic in America that led to 18,000 deaths last year, he noted.

The People's Republic of China on Monday followed through on a pledge, though short of immediacy, it made in December to list the drug as a controlled substance. The new rule goes into effect May 1st.

Cramer said he doesn't see this as a win for President Donald Trump, who has called on his counterpart to hold fentanyl "distributors and pushers" accountable by death penalty. The Chinese, however, have blamed the U.S. for its abuse.

"There was no serious push by the Communist Party [of China] to put a stop to this. Every time China's banned one kind of fentanyl, their manufacturers just change the formula a little bit to something that's now legal," Cramer said. "This new ban is supposed to change all of that, but given China's track record when it comes to upholding international agreements, consider me skeptical."

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Cramer said investors can get an idea of how the market could perform in the second quarter by understanding how the major averages rallied during the first quarter of the year.

The Nasdaq had the biggest gain — 16 percent — to open the year. The S&P 500 rallied 13.1 percent and the Dow Jones Industrial Average added 11 percent in the first quarter. The indexes all added more or less 1.2 percent during Monday's session.

"I think the stock market benefited from a dearth of new supply" due to the government shutdown, its impact on IPOs and the high-volume of company stock buyback programs, the "Mad Money" host said. "I think this market can go higher as long as we don't get overwhelmed with new supply from this wave of IPOs, because I think the valuations are still too low for so many stocks, like we see from the top five performers in the Dow."

It was a "fabulous windfall for investors" until Friday, Cramer said, when Lyft went public at $72 a share and traded as high as $88. The share price fell to nearly $69 at Monday's close.

Cramer took a look at the Dow's highest-performing stocks in the first quarter to predict the future.