• After shares of QuantumScape, Luminar, Arrival and Canoo made big gains in a short timeframe, CNBC's Jim Cramer is recommending investors trim their holdings.
• "Speculative stocks can get overheated, which is why it's important to take profits while you have them," the "Mad Money" host said.
• "These stocks have gotten out of control, so I'm begging you to take something off the table," he said.

In a classic lesson of buying low and selling high, CNBC's Jim Cramer on Thursday recommended investors trim their holdings in a number of speculative stocks he recently said are worth owning.

After some of the stock picks put up triple-digit gains in a short timeframe, he advises trading at least the cost basis, or the value invested in an asset.

"I'm one of the few commentators who will ever endorse buying speculative stocks … but you have to be a responsible speculator," the "Mad Money" host said. "Speculative stocks can get overheated, which is why it's important to take profits while you have them."

Since October, Cramer has endorsed four electric car startups coming public through what's known as SPACs, or special purpose acquisition companies. SPACs are formed to raise money through investors to buy out a private entity, making it a publicly traded company.

In late October, Cramer covered QuantumScape, which develops solid-state lithium-metal batteries. Since then, the stock has increased more than fivefold, a nearly 61-point run to its $76.61 close on Thursday.

Luminar, a guidance technology manufacturer for self-driving vehicles, was recommended by Cramer just over a week ago. After the Dec. 2 close, he said the stock was a buy under $15 per share, though the opportunity never presented itself. Shares surged more than doubled in the matter of four trading days. Since Tuesday's $41.80 close, the stock has lost 18% of value falling to $34.17.

Shares of CIIG Merger, the blank check firm targeting British electric car maker Arrival in a takeover, surged to a peak close of $41.03 on Monday after Cramer, who called it a buy at $17.50, considered it on "Mad Money" a week ago. The stock only went up from its $23.73 close last Thursday, though it has come down to $34.80, a 15% fall from levels earlier this week.

Canoo, the membership-based electric car company going public through a SPAC called Hennessy Capital Acquisition Corp IV, was offered by Cramer as a buy last Friday at $15.64. The stock closed at a high of $26.33 Thursday for a gain of 68% in four sessions.

"These stocks have gotten out of control, so I'm begging you to take something off the table," Cramer said. "You can always get back in at lower levels, and I'm very confident that lower prices could be in the cards."

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