Learn Hardcore German: Diese Nebenwirkung ist nur leicht, deshalb bleibe ich trotzdem ruhig. - This side effect is only mild, therefore I remain calm anyway.

In the sentence, Nebenwirkung is the subject of the verb ist, so it’s in the nominative case.
Therefore, the correct demonstrative determiner is diese (feminine nominative singular), not dieser (masc./fem. gen./dat.) or dieses (neuter or genitive masc./neut.).

What exactly does Nebenwirkung mean, and is it always medical?

Literally, Nebenwirkung is a compound:

neben = beside, additional, secondary
Wirkung = effect

So it means secondary effect, i.e. side effect.

Usage:

It is very common in medical contexts: side effects of medication, treatments, vaccines, etc.
- Die Nebenwirkungen dieses Medikaments sind mild.
It can also be used more generally for side effects of actions or events, not only medical:
- Eine Nebenwirkung dieser Reform ist steigende Arbeitslosigkeit.
  (A side effect of this reform is rising unemployment.)

But in everyday language, many people first associate Nebenwirkung with medicine.

In ist nur leicht, why is leicht used here, and not something like einfach?

Both leicht and einfach can translate to light/easy, but they’re used differently.

leicht:
- physically light: Der Koffer ist leicht.
- not severe / mild: Die Schmerzen sind leicht.
- easy (often about difficulty): Die Übung ist leicht.
einfach:
- simple, uncomplicated: Das ist eine einfache Aufgabe.
- can also mean “just / simply”: Ich will einfach nur schlafen.

In the sentence Diese Nebenwirkung ist nur leicht, leicht means mild / not severe.
einfach would sound wrong here, because we’re not talking about simplicity but about the intensity of the side effect.

You could say Diese Nebenwirkung ist nur mild, which is also correct and common, but leicht is very natural here.

What does nur add in ist nur leicht? Could we leave it out?

nur means only / just here and expresses downplaying or limiting:

Diese Nebenwirkung ist leicht.
= The side effect is mild. (neutral statement)
Diese Nebenwirkung ist nur leicht.
= The side effect is only mild / just mild. (emphasizes “not bad”)

So nur adds the nuance: It’s nothing serious, don’t worry.

Grammatically, you can leave it out, but you slightly change the tone:

With nur: reassuring, minimizing the problem.
Without nur: more neutral, more factual.

Why is there a comma before deshalb? Is deshalb a conjunction?

There are two main clauses here:

Diese Nebenwirkung ist nur leicht,
deshalb bleibe ich trotzdem ruhig.

German allows you to connect two main clauses with a comma, especially when you introduce the second with an adverb like deshalb, trotzdem, dann, außerdem, etc.

deshalb is not a subordinating conjunction like weil, dass, obwohl, etc.
It is an adverbial connector (a sentence adverb) meaning therefore / for that reason.

Because both parts are full independent clauses, you separate them with a comma.

If deshalb is not a conjunction, why is the word order deshalb bleibe ich and not deshalb ich bleibe?

German main clauses obey the verb‑second rule (V2): the finite verb must be in second position.

In the second clause:

deshalb is in the first position (a connector/adverb).
The verb bleibe must therefore come second.
The subject ich comes after the verb.

So the structure is:

Position 1: deshalb
Position 2: bleibe (finite verb)
Rest of the sentence: ich trotzdem ruhig

You could also say:

Ich bleibe trotzdem ruhig. (now ich is first, so bleibe is second.)

But once you put deshalb first, the verb must immediately follow.

What’s the difference between deshalb and trotzdem? They both look like linking words.

They both link clauses, but they express different relationships:

deshalb = therefore, for that reason (cause → effect)
- Es ist kalt, deshalb trage ich eine Jacke. (It’s cold, therefore I’m wearing a jacket.)
trotzdem = nevertheless, despite that, anyway (contrast / concession)
- Es ist kalt, trotzdem gehe ich schwimmen. (It’s cold, nevertheless I go swimming.)

In your sentence:

Diese Nebenwirkung ist nur leicht,
= situation / background
deshalb bleibe ich trotzdem ruhig.
= my reaction to that situation (deshalb = that’s why; trotzdem = in spite of having a side effect at all)

So deshalb expresses the reason why the speaker can remain calm: it’s only mild.
trotzdem emphasizes that even though there is a side effect, the speaker still stays calm.

Why do we have both deshalb and trotzdem here? Isn’t one of them enough?

They each highlight a different nuance:

deshalb: “for this reason” (because it’s mild)
trotzdem: “in spite of that” (in spite of the side effect existing)

Compare:

Diese Nebenwirkung ist nur leicht, deshalb bleibe ich ruhig.
→ It’s mild, so I stay calm. (pure cause and effect)
Diese Nebenwirkung ist nur leicht, trotzdem bleibe ich ruhig.
→ Even though there is a side effect (but it’s mild), I stay calm anyway. (more contrast)
Diese Nebenwirkung ist nur leicht, deshalb bleibe ich trotzdem ruhig.
→ Combines both:
- Reason: because it’s mild (deshalb),
- And emphasis: I still don’t let it upset me (trotzdem).

So using both is not redundant; it makes the speaker’s attitude more explicit.

Can trotzdem be placed in another position, like deshalb bleibe ich ruhig trotzdem?

In the given sentence, natural options are:

deshalb bleibe ich trotzdem ruhig. ✅ (standard, very natural)
deshalb bleibe ich ruhig. ✅ (without trotzdem)
trotzdem bleibe ich ruhig. ✅ (if you drop deshalb and start with trotzdem)

Within the clause ich bleibe trotzdem ruhig, the usual positions are:

Ich bleibe trotzdem ruhig. ✅
Ich bleibe ruhig trotzdem. ❌ (sounds wrong/very unusual)

The general rule:

Sentence adverbs like trotzdem prefer to stand early in the “middle field”, usually right after the subject or after another initial element.

So use:

Ich bleibe trotzdem ruhig.
Deshalb bleibe ich trotzdem ruhig.

but avoid ruhig trotzdem at the end.

Why is it bleibe ich and not ich bleibe after the comma?

Same reason as before: the V2 (verb‑second) rule in main clauses.

Second clause:

deshalb is placed first for emphasis / linkage.
The finite verb bleibe must be second.
The subject ich follows the verb.

So:

deshalb (1st) – bleibe (2nd) – ich trotzdem ruhig (rest)

If you don’t start with deshalb, you’d say:

Ich bleibe trotzdem ruhig. (Now ich is first, bleibe second.)

You must not write:

… deshalb ich bleibe trotzdem ruhig. ❌
(This breaks the verb‑second rule.)

Does ruhig here mean “calm” or “quiet”? How should I understand ruhig bleiben?

ruhig has two common meanings:

quiet / silent:
- Sei ruhig! = Be quiet!
- Das Baby schläft ruhig. = The baby is sleeping peacefully/quietly.
calm / composed (emotionally):
- Bleib ruhig! = Stay calm!
- Er reagierte ganz ruhig. = He reacted very calmly.

In deshalb bleibe ich trotzdem ruhig, the intended meaning is emotionally calm, not “silent”.
So ruhig bleiben here = to remain calm / to keep one’s cool.

Is ruhig bleiben a fixed expression, and how is it different from ruhig sein?

Both are correct, but the nuance is slightly different:

ruhig sein = to be calm/quiet (state)
- Ich bin ruhig. = I am calm/quiet.
ruhig bleiben = to stay calm, to continue being calm (emphasis on not losing calmness)
- Bleib ruhig! = Don’t lose your calm / keep calm.

In this sentence, bleibe ich ruhig focuses on maintaining composure even though there is a side effect. That’s why bleiben fits very well.

Could we also say Diese Nebenwirkung ist nur eine leichte, deshalb bleibe ich ruhig or something like that?

More natural alternatives using an attributive adjective would be:

Es ist nur eine leichte Nebenwirkung, deshalb bleibe ich trotzdem ruhig.
Ich habe nur eine leichte Nebenwirkung, deshalb bleibe ich trotzdem ruhig.

Your original pattern Diese Nebenwirkung ist nur leicht uses leicht as a predicate adjective (after the verb sein); that’s very idiomatic.

Saying Diese Nebenwirkung ist nur eine leichte (with eine leichte standing alone) sounds unfinished and unusual; you’d normally complete it:

… ist nur eine leichte Nebenwirkung. ✅

So you can choose:

Predicate adjective: Diese Nebenwirkung ist nur leicht.
Attributive adjective: Es ist nur eine leichte Nebenwirkung.

Both are grammatically fine, just different structures.

Could we replace deshalb with weil and say weil die Nebenwirkung nur leicht ist, bleibe ich ruhig?

Yes, but the structure and style change:

With deshalb (two main clauses):
- Diese Nebenwirkung ist nur leicht, deshalb bleibe ich trotzdem ruhig.
- Both clauses are independent; deshalb is an adverb, verb stays in 2nd position.
With weil (one main + one subordinate clause):
- Weil die Nebenwirkung nur leicht ist, bleibe ich trotzdem ruhig.
- weil is a subordinating conjunction → verb goes to the end of the subordinate clause (ist at the end).

Meaning-wise, both express a reason, but:

deshalb sounds a bit more neutral and written-style in some contexts.
weil is extremely common in spoken language and everyday German.

Both are perfectly correct; they just use different grammar patterns.

Could ruhig also refer to physical silence here, like “I stay quiet”?

Context decides, but with Nebenwirkung and no mention of speaking/noise, German speakers will naturally interpret ruhig here as calm / not worried.

If the intended meaning were “I stay quiet (I don’t say anything)”, you’d normally make that clearer:

… deshalb sage ich nichts und bleibe still.
… deshalb bleibe ich still.

still bleiben and ruhig bleiben can both mean “to stay quiet”, but in a medical or emotional context, ruhig bleiben is almost always understood as “stay calm”.