In the clinical sense, probably not. Was he at times so suspicious of others that it effected his decision making? I think we could reasonably argue that. Whether he had cause or not probably depends on what period you're thinking of.

Stephen Kotkin in his Stalin biography comes down pretty hard against the idea that Stalin had some kind of behavioural disturbance (be that paranoia, psycopathy or what have you), noting that none of Stalin's allies or enemies seems to have really noted this at the time. But he does reinforce that Stalin's behavour was a bit paranoid for an assortment of reasons - like his political career starting in the underground, as well as events that took place in the mid 1920s.

Those incident/s in the 1920s are of note in terms of whether Stalin had 'sufficient cause' - because there were indeed instances where Stalin's enemies, and allies, played around to some extent with plans to get rid of or undermine him. So if Stalin were acting paranoid in this era wouldn't this be legitimate? The correspondence Kotkin references to me is interesting this respect because looking at some of those incidents, like where Bukharin and others were discussing Stalin's 'futue' during the so-called cave conference. Stalin, having become aware of this, doesn't so much flip out and start jumping at shadows as we might stereotypically assume someone with paranoia might once they discover that maybe they're right. Instead Stalin makes a great show of having hurt feelings, feeling under appreciated etc.

But of course when we're talking about Stalin's paranoia, we're probably more wondering about Stalin's state of mind during the purges, the great famine and similar. As noted above, Stalin's behaviour by that point might have been shifted somewhat by the bitter infighting with Trotsky and even his own allies. This might cause him to disregard reports that tell him things he doesn't 'trust' (ie. that there really isn't enough grain, that there aren't really that many people planning to destroy the party-state etc.) or motivate him to act - like the purge of the Red Army, which kicked off the purges.

But we should next consider whether paranoia was Stalin's only motivation in these acts, or inaction. For example returning to Kotkin he relates the manner in which Stalin would 'uncover' plots in various locations he was sent to during the Civil War. For example Stalin makes these seemingly hysterical reports of fifth columnists in Tsaritsyn and has 'opponents' in the town arrested. But Stalin in all probability didn't just do this because he believed people were out to get him - Kotkin suggests that Stalin would have seen these purges as a mobilising tool. For example the media reporting around these arrests would be a way of getting people worked up about 'enemies' (which depending on the tone of reporting, might include more mundane foes like slacking bureaucrats), and perhaps to act on their own initiative. Stalin may geuninely have believed arresting people who weren't in line with his objectives would strengthen the political situation. In the Tsaritsyn case, it was even suggested there were material incentives - reports of a large amount of gold arriving from Moscow, sent to the 'faction' subject to arrests, apparently went missing (perhaps to boost Stalin's literal or figurative war chest?).

So long story short Stalin at times behaved in a paranoid way without justification. There doesn't seem to be much legitimate evidence to support the official 'charges' that came with the purges, and even alternative explanations for the purge's motivations, like J. Arch Getty's, still don't align well with what was going on. But paranoia alone probably doesn't adequetely explain why he did what he did. After all a lot of paranoid people just refuse to leave the house or similar - Stalin by comparison was more proactive.

While I think of it, having mentioned Getty, consider also the possibility that at times large sections of the party would have been paranoid for similar reasons. This would tend to reinforce any paranoid thinking, as well as create a possible drive to initiate policy that many might favour.

Some quick references:

• Stephen Kotkin: Stalin Vol 1 - The Paradoxes of Power

• J. Arch Getty - The Road to Terror